GFCI & ALCI Transformers

L&H components ltd supply wound GFCI differential transformers to those customers who do not want to wind and assemble their own components. The cores used in differential transformers reliably measure ground faults of 5mA, 10mA, 30mA or more over the temperature range from -35oC to +80oC as required by UL Standard 943. This is accomplished through the use of high permeability core materials in ring form. The high permeability is maintained after low resistance faults, which could drive the core into saturation and leave it in the remanent state.

The GFCI differential transformers are normally wound with 1000 turns of 38 AWG to 40 AWG magnet wire and are placed in pinned core holders for easy circuit board mounting. The pins can be bent for horizontal or vertical mounting depending on the construction of the GFCI device.

The table below is a list of standard GFCI differential transformers (click on part number for drawing):

ALCI and Arc Fault sensor transformers with a temperature stability of 0oC to 80oC are available in all of the above parts. Please indicate this requirement upon ordering.

A Ground to Neutral Short Detection Coil is required by UL Standard 943 to meet the tripping of the GFCI device when the resistance between the ground and neutral wire drops below a minimum value. The generally accepted method to accomplish this is to induce an isolated voltage in the neutral wire, which when shorted to the ground, will produce a signal in the sensor core and trip the device. Either 60 Hz inductors or the dormant oscillator approach as described in the IC manufacturer’s circuit information are used. For the dormant oscillator approach we recommend any of the above part numbers utilising the ferrite core F3XXX series.